The multiple nuclei model, developed by Chauncy Harris and Edward Ullman in 1945, is an urban land-use model proposing that cities grow around several separate centers of activity (nuclei) rather than a single central business district, one of the internal city structure models in AP Human Geography Topic 6.5.
The Multiple Nuclei Model is Chauncy Harris and Edward Ullman's 1945 answer to a question the older city models couldn't handle. What if a city doesn't have just one center? In their model, a city grows around several independent nuclei, like a CBD, an industrial district near a port or rail line, a university area, an airport zone, and outlying shopping districts. Each nucleus attracts compatible land uses (a university pulls in bookstores and student housing) and repels incompatible ones (heavy industry and wealthy neighborhoods stay far apart).
Think of it this way. The Burgess concentric zone model assumes everything radiates outward from one downtown. Harris and Ullman looked at mid-20th-century American cities, shaped by cars and trucks instead of just a central rail hub, and saw something messier. Activities cluster wherever it makes sense for them, so the city ends up as a patchwork of specialized districts rather than neat rings. It's named in the CED (EK PSO-6.D.1) as one of the core models you use to explain the internal structure of cities, alongside Burgess, Hoyt, the galactic city model, and bid-rent theory.
This term lives in Unit 6 (Cities and Urban Land-Use Patterns and Processes), specifically Topic 6.5, where learning objective 6.5.A asks you to explain the internal structure of cities using models and theories. The CED lists "the Harris and Ullman multiple-nuclei model" by name, so it's fair game on any MCQ about urban structure. It also sets up later Unit 6 topics. The model's car-enabled, decentralized growth pattern is exactly what produces urban sprawl and infrastructure challenges (Topics 6.7, 6.8, and 6.11), and it's the conceptual ancestor of the galactic city model and edge cities. If you can explain why a city would develop multiple nuclei, you can explain a lot of modern suburbanization.
Keep studying AP Human Geography Unit 6
Burgess Concentric Zone Model (Unit 6)
The multiple nuclei model is basically a rebuttal to Burgess. Burgess (1920s) drew the city as rings around one CBD; Harris and Ullman (1945) said the automobile broke that pattern, letting activity centers pop up all over the city instead of stacking around downtown.
Edge City (Unit 6)
Edge cities are the multiple nuclei idea taken to its modern extreme. Those suburban nodes of offices, malls, and entertainment near highway interchanges are nuclei that grew so large they rival the original CBD, which is why the galactic city model is often described as the multiple nuclei model stretched across a metro area.
Urban Sprawl (Unit 6)
When growth no longer has to anchor to one downtown, cities spread outward fast and unevenly. The decentralization the multiple nuclei model describes feeds directly into the sprawl and sustainability problems covered in Topics 6.8 and 6.11.
Infrastructure in Urban Development (Unit 6)
Each nucleus forms around infrastructure, like a port, rail yard, airport, or highway interchange. That's EK IMP-6.B.1 in action: where infrastructure goes directly shapes the spatial pattern of economic development.
Multiple choice is where this model shows up most. A classic stem describes a city with "multiple specialized activity centers that function independently from the traditional CBD" and asks which model fits, or it lines up Burgess, Hoyt, Harris-Ullman, and the galactic city model and makes you match the description to the right one. Your job is to spot the giveaway language. "Concentric rings" means Burgess, "sectors or wedges along transport routes" means Hoyt, and "multiple independent centers" means Harris and Ullman. No released FRQ has required this exact term, but FRQs on urban land use often let you bring in any internal city structure model, and naming the multiple nuclei model (with Harris and Ullman attached) is an easy way to show command of CED vocabulary when explaining decentralized growth or comparing models.
Both models break from Burgess's neat rings, so they get mixed up. The difference is how growth spreads. Hoyt's sector model (1939) still has ONE center, with land uses extending outward in wedges along transportation corridors like rail lines. The multiple nuclei model (1945) drops the single-center assumption entirely; activities cluster around several separate, independent nodes. Quick test: one downtown with pie slices means Hoyt, several scattered centers means Harris and Ullman.
The multiple nuclei model, created by Chauncy Harris and Edward Ullman in 1945, says cities develop around several independent centers of activity rather than a single CBD.
Each nucleus attracts compatible land uses and repels incompatible ones, so similar activities cluster together (industry near ports, student housing near universities) while conflicting uses stay apart.
The model reflects the automobile era. Cars and trucks freed businesses from depending on one central downtown, which the ring-based Burgess model assumed.
It is named in EK PSO-6.D.1 as one of the models for explaining the internal structure of cities, alongside Burgess, Hoyt, the galactic city model, and bid-rent theory.
The multiple nuclei model is the conceptual foundation for edge cities and the galactic city model, which apply the same multi-center logic to entire suburban metro areas.
On MCQs, the phrase "multiple centers of activity" or "independent from the CBD" points to Harris and Ullman, while "rings" points to Burgess and "wedges" points to Hoyt.
It's a 1945 urban land-use model by Chauncy Harris and Edward Ullman proposing that cities grow around multiple separate centers (nuclei) like a CBD, industrial districts, universities, and airports, instead of expanding outward from a single downtown. It's one of the internal city structure models in Topic 6.5.
The Burgess concentric zone model (1920s) has one CBD with land uses arranged in rings around it. The multiple nuclei model has no single dominant center; activities cluster around several independent nodes scattered across the city. Burgess assumes growth radiates from one point, Harris and Ullman assume it doesn't.
Yes, but the CBD is just one nucleus among several, not the organizing center of the whole city. Other nuclei, like industrial parks, universities, and outlying business districts, function independently of it.
Harris and Ullman built the model from mid-20th-century American cities shaped by automobile travel, and large sprawling metros like Los Angeles are the classic example. The key is that car-based transportation let activity centers form away from the original downtown.
No, but they're related. The galactic city (peripheral) model extends the multiple nuclei idea to the metro scale, with edge cities orbiting the original city along beltways. The CED lists them as separate models in EK PSO-6.D.1, so know both.
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